1. Field of the Invention
The present disclosure is related to a unique, catalytic material containing zeolite embedded in a catalyst support, and particularly to a microporous zeolite embedded in a mesoporous support.
2. Background of the Art
Many of today's hydrocarbon processing technologies are based on zeolite catalysts. Zeolite catalysts are well known in the art and possess well-arranged pore systems with uniform pore sizes. However, these materials tend to possess either only micropores or only mesopores, in most cases only micropores. Micropores are defined as pores having a diameter of less than about 2 nm. Mesopores are defined as pores having a diameter ranging from about 2 nm to about 50 nm. The small micropores limit external molecules to access the catalytic active sites inside of the micropores or slow down the diffusion process to the catalytic active sites. Many catalytic reactions of hydrocarbons are mass-transfer limited, so the effective utilization of the catalyst is reduced. One solution is to reduce the catalyst particle size, thereby shortening the diffusion path and increasing the external surface of the catalyst particles.
In practice, the small zeolite catalyst particles cannot be directly used because the dust-like material is difficult to handle, and it would create a pressure drop problem in a fixed bed reactor. As such, the zeolites are usually mixed with an inorganic oxide and extruded into a certain shape and size. The calcined, finished catalyst then has good physical integrity and a porous structure. However, depending upon the specific reaction, the binder can impose a mass-transfer limitation to the zeolite particles buried inside the binder. If the less porous binder can be replaced by a highly porous support, the accessibility of external molecules to active sites in zeolites will be increased.
It is highly desired to have a catalyst with ideal pore size distribution, which will facilitate transport of the reactants to active catalyst sites and transport of the products out of the catalyst.